Process for producing aromatic hydroxycarboxylic acids

ABSTRACT

This invention provides a process for selectively producing aromatic hydroxycarboxylic acids, which comprises subjecting a liquid mixture consisting of a polycyclic aromatic hydrocarbon, an alkali metal salt of an aromatic hydroxy compound and a free aromatic hydroxy compound to a reaction with carbon dioxide. The process permits the production of the intended product with enhanced selectivity.

FIELD OF TECHNOLOGY

This invention relates to a process for selectively producing aromatichydroxycarboxylic acids, which comprises liquefying an alkali metal saltof an aromatic hydroxy compound with an added aromatic hydroxy compound,followed by reaction with carbon dioxide in a liquid-liquid mixture witha medium.

BACKGROUND TECHNOLOGY

Aromatic hydroxycarboxylic acids, particularly p-hydroxybenzoic acid,salicylic acid, 2-hydroxy-3-naphthoic acid, etc., have long been knownfor their usefulness as raw materials for the production of antisepticand antifungal agents, pharmaceuticals, dyestuffs, pigments and thelike, and in recent years, have furthermore acquired increasinglygreater importance not only as starting compounds for the synthesis ofagricultural chemicals, color developing agents for thermosensitiverecording paper, etc. but also as monomers for aromatic polyesters.

These aromatic hydroxycarboxylic acids have conventionally been producedby means of the so-called Kolbe-Schmitt process involving a vapor-solidphase reaction of an alkali metal salt of aromatic hydroxy compound withcarbon dioxide. Lately, one of the present inventors has improved thesaid vapor-solid phase reaction process into the liquid-solid phasereaction process making use of a suspension phase, and thus, there hasbeen established a process which permits an industrial-scale,mass-production of such aromatic hydroxycarboxylic acids [refer to thespecification of Patent Application No. 39281/1983 (Laid-Open PatentPublication No. 164751/1984)].

DISCLOSURE OF THE INVENTION

The present inventors, with a specific view to further improving theprocess, carried out repeated research, and found that diaryl or triarylbased polycyclic aromatic hydrocarbons remaining liquid at ambienttemperature and showing a boiling point of not less than 250° C. canproduce excellent effects under conditions of an added aromatic hydroxycompound. The finding has led to the completion of this invention.

This invention is directed to a process for selectively producingaromatic hydroxycarboxylic acids, characterized in that the said processcomprises allowing a liquid mixture consisting of a polycyclic aromatichydrocarbon, alkali metal salt of an aromatic hydroxy compound and freearomatic hydroxy compound to undergo reaction with carbon dioxide.

The present invention can achieve the following effects:

(1) The media of this invention can suspend thoroughly alkali metalsalts of aromatic hydroxy compounds, which permits the completedehydration of such alkali metal salts of aromatic hydroxy compounds tobe performed promptly and at relatively low temperatures. Consequently,therecan be easily obtained anhydrous alkali metal salts of aromatichydroxy compounds as a raw material, which, when admixed with aromatichydroxy compounds and the reaction medium and subjected to a reactionwith carbon dioxide, contribute to outstandingly improved yields of theobjective compound to be obtained in such a reaction.

(2) A mixture consisting of an anhydrous alkali metal salt of aromatichydroxy compound, aromatic hydroxy compound and a reaction medium hastheir components all kept in the liquid form and suspended thoroughlyand uniformly under reaction conditions, and can be transported in aquantitative manner, which secures the constant reaction yield in thecontinuous production process.

(3) The improvement of both yield and selectivity is of utmostimportance in the Kolbe-Schmitt reaction, where the production ofisomers is always involved and basically inevitable owing to theprinciple of orientation in the aromatic substitution reaction. In theconventional Kolbe-Schmitt reaction processes, the production of isomerstakes place, in spite of the reaction conditions, inclusive oftemperature and pressure, being optiomally set to minimize the isomerproduction. However, this invention constitutes a process which keepsthe starting material system in the liquid form under reactionconditions and consequently suppresses markedly the production ofisomers, permitting the objective compound to be formed in theoutstandingly improved selectivity, as compared with the solid-liquidsuspension system in the conventional processes.

Thus, in the said reaction where aromatic hydroxycarboxylic acids areformed, the supplementary addition of an aromatic hydroxy compoundallows the mutual affinity among three compounds of the aromatic hydroxycompound, the alkali metal salt of an aromatic hydroxy compound and thereaction medium to be optimally regulated, which can control theorientation direction in the said reaction and can also enhanceoutstandingly the selectivity.

(4) The reaction media exhibit a high degree of affinity not only foraromatic hydroxy compounds but also for alkali metal salts of aromatichydroxy compounds, and when mixed with them to form a liquid-liquidmixture of the three components, provide a highly good suspension state,resulting in improvement in the rate of reaction step and the yield ofthe objective compound.

(5) The process of this invention, which suppresses the conversion intotar of the reaction product in the reaction step and allows the tarryby-products to dissolve in the reaction medium layer, minimizes thecontamination of tarry substances into a layer of the alkali metal saltof aromatic hydroxy compound, thus preventing reductions in reactionrate and in yield and proportion of the desired compound owing tocontamination of tarry substances.

(6) The above-described reaction media, because of their increaseddistribution ratio for aromatic hydroxy compounds, allow aromatichydroxy compounds to migrate into the water layer to a minimal extent,and consequently facilitate the recovery of aromatic hydroxy compounds.This, coupled with a reduced degree of contamination of tarry substancesinto the water layer, eliminates the extraction step with organicsolvents, etc. for the water layer in the finishing treatment step,while securing the direct production of the objective compound from thewater layer.

(7) The above-mentioned reaction media demonstrate excellent thermalstability at increased temperatures even in the presence of alkali metalsalts of aromatic hydroxy compounds. Since the loss as a result ofthermal degradation is small, it is economically advantageous.

(8) The aforesaid reaction media not only enhances the yield andpercentage obtained of the intended product, but also since the mediathemselves possess superior thermal stability, the production ofimpurities is reduced, and this facilitates the treatment procedure inthe finishing treatment step.

(9) The above-described reaction media, with their higher boilingpoints, usually bring about no pressure increase owing to vapourpressure of solvent in the reaction step, and offer consequentlyadditional advantage that the reaction vessel can be designed towithstand merely the pressure of carbon dioxide.

The polycyclic aromatic hydrocarbons which are used in this inventioninclude, for example, diaryls, diarylalkanes, triaryls, triarylalkanesor their hydrogenated compounds or mixtures thereof; as preferredexamples, among others, there may be mentioned1-phenyl-1-(2,3-dialkylphenyl)-alkanes, triphenyl, dibenzyltoluene,hydrogenated triphenyls or mixtures thereof, and those having a boilingpoint of not less than 250° C. are desirable.

The alkali metal salts of aromatic hydroxy compounds include, forexample, potassium phenolate, sodium phenolate or sodium 2-naphtholate.

In the Kolbe-Schmitt reaction process, the complete dehydration of a rawmaterial, an alkali metal salt of aromatic hydroxy compound, constitutesone of the most important problems, and inadequate dehydration of theabove-described raw material results in a marked decrease in reactionyield. The above raw material can be produced in accordance with theconventional method by the reaction of phenol or 2-naphthol with analkaline potassium or sodium compound, such as hydroxides, carbonatesand hydrogencarbonates of potassium or sodium, and it is particularlyadvantageous to dehydrate the resulting alkali metal salt of aromatichydroxy compound in the presence of the above-mentioned reaction medium.

According to this invention, the reaction of an alkali metal salt ofaromatic hydroxy compound with carbon dioxide is carried out at atemperature of not lower than 100° C., preferably 120° to 300° C.,particularly 150° to 300° C., and at a carbon dioxide pressure of nothigher than 30 kg/cm² (G), preferably 1 to 15 kg/cm² (G), particularly 2to 10 kg/cm² (G). The addition amount of the aromatic hydroxy compoundis normally not less than 0.05 mole per mole of alkali metal salt ofaromatic hydroxy compound, preferably 0.1 to 2 mole. The usage amount ofthe reaction medium is normally not less than 0.5 part by weight againsteach part by weight of alkali metal salt of aromatic hydroxy compound,preferably 0.5 to 10 parts by weight, particularly 1 to 5 parts byweight. The reaction can be conducted either by the batch or continuousprocess, but it is desirable to carry out the reaction by the continuousprocess. As the reaction time or the residence time, there can besuitably selected any length of time ranging from several minutes to 15hours, preferably 10 minutes to 10 hours, particularly 20 minutes to 10hours.

The finishing treatment can be conducted, for example, by the followingprocedure. After addition of water to the reaction mixture, the reactionmedium layer is separated out, and the dissolved aromatic hydroxycompound can be recovered with a solution of an alkaline potassium orsodium compound as an alkali metal salt of the aromatic hydroxycompound, which is then subjected to reuse. The separated water layer isadjusted in liquid nature with dilute or concentrated sulfuric acid, andthe dissolved aromatic hydroxy compound is then extracted with use oftoluene or xylene as a reaction medium or organic solvent, as the casemay be. The organic solvent layer is washed with a solution of analkaline potassium or sodium compound to recover it as an alkali metalsalt of the aromatic hydroxy compound for reuse as a starting compound.Alternatively, the whole amount of the organic solvent layer can bedistilled off to separate into the organic solvent and the aromatichydroxy compound, with the latter being reused as a starting compound.These finishing treatment procedures can be suitably selected.

INDUSTRIAL UTILIZABILITY

The present invention can offer various advantages as described aboveunder the items (1) through (9), and is of outstandingly great,industrial value.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic flow diagram illustrating the mode of carrying outthis invention, wherein the reference numerals 1 and 4 each designate astirring tank; the numeral 2 a reaction vessel; the numeral 3 a heatexchanger; the numeral 5 a separating tank; the numeral 6 a pHadjustment tank; the numeral 7 an extractor; and the numeral 8 an acidprecipitation tank, respectively.

PREFERRED MODE OF CARRYING OUT THE PRESENT INVENTION EXAMPLE 1

In a pressure reaction vessel were charged 100 g of sodium phenolate, 35g of phenol and 400 g of a mixture of hydrogenated triphenyls, and areaction was allowed to proceed at 250° C. and at a carbon dioxidepressure of 7 kg/cm² (G) for 20 minutes, with stirring The reactionmixture was cooled and charged into 200 ml of water, followed byseparation into the reaction medium layer and the water layer at 60° C.The water layer was extracted with 50 g of xylene, and the phenol wasrecovered with an aqueous potassium hydroxide solution from the reactionmedium and extraction medium layers. After recovery of phenol, the waterlayer was made acid with dilute sulfuric acid to give 80.8 g ofp-hydroxybenzoic acid (having a purity of 100%), with neither salicylicacid nor isophthalic acid being detected as an isomer. The yield basedon potassium phenolate was 77.3%, and the recovered phenol was 21.8 g,with the selectivity being 99.7%.

EXAMPLE 2

In a pressure reaction vessel were charged 100 g of sodium phenolate, 40g of phenol and 400 g of 1-phenyl-1-(2,3-dimethylphenyl)-ethane, and areaction was allowed to proceed at 170° C. and at a carbon dioxidepressure of 10 kg/cm² (G) for 2 hours, with stirring. The reactionmixture was cooled and charged into 500 ml of water, followed byseparation into the reaction medium layer and the water layer at 90° C.The water layer was extracted with 50 g of xylene, and the phenol wasrecovered with an aqueous sodium hydroxide solution from the reactionmedium and extraction medium layers. After recovery of phenol, the waterlayer was made acid with dilute sulfuric acid to give 94.3 g ofsalicylic acid, with neither p-hydroxybenzoic acid nor isophthalic acidbeing detected as an isomer. The yield based on sodium phenolate was90.2%, and the recovered phenol was 57 g, with the selectivity being98.5%.

EXAMPLE 3

In a pressure reaction vessel were charged 166 g of sodium2-naphtholate, 72 g of 2-naphthol and 498 g of hydrogenated triphenyl,and a reaction was allowed to proceed at 260° C. and at a carbon dioxidepressure of 5 kg/cm² (G) for 3 hours, with stirring. The reactionmixture was charged into 800 ml of water, and the resulting mixture wasadjusted to a pH 5.5 with sulfuric acid, followed by separation into thereaction medium layer and the water layer at 85° C. The 2-naphthol wasrecovered with an aqueous sodium hydroxide solution from the reactionmedium layer. After recovery of 2-naphthol, the water layer was adjustedto a pH 2.0 with sulfuric acid at the same temperature, cooled to 40° C.and subjected to filtration to give 89.3 g of2-hydroxynaphthalene-3-carboxylic acid. The product was found to containonly 0.1% of 2-hydroxynaphthalene-6-carboxylic acid, with no trace of2-hydroxynaphthalene- 1-carboxylic acid. The yield based on sodium2-naphtholate was 47.5%, with the selectivity being 99.3%.

EXAMPLE 4

A finishing treatment was carried out continuously, while employing thefacilities as shown in the drawing. On an hourly basis, 83 kg of sodium2-naphtholate, 42 kg of 2-naphthol and 166 kg of a mixture ofhydrogenated triphenyls were fed to a stirring tank 1, followed bystirring and suspension. The resulting suspension mixture was suppliedat a rate of 291 kg/hr to a reaction vessel 2 maintained at a carbondioxide pressure of 6 kg/cm² (G), and a reaction was allowed to proceedat 260° C., with the residence time being kept at 3 hours. The reactionmixture flowing out of the reaction vessel 2 was cooled with a heatexchanger 3, and mixed with water fed at a rate of 420 1/hr in astirring tank 4, and the resulting mixture was regulated at atemperature of 85° C. and transferred to a separating tank 5, followedby separation into the reaction medium layer and the water layer at 85°C. From the upper reaction medium layer, the 2-naphthol was recovered assodium naphtholate with use of a recovery apparatus (not shown in thedrawing). The lower water layer was adjusted in a pH adjusting tank 6 toa pH 5.5 with dilute sulfuric acid and transferred to an extractor 7,where the 2-naphthol and tar were extracted with 2000 liters of xylene.From the xylene layer, there were recovered the xylene and 2-naphthol byuse of a vacuum distillation apparatus (not shown in the drawing). Thewater layer flowing out of the extactor 7 was transferred to an acidprecipitation tank 8, and adjusted to a pH 2.0 with dilute sulfuric acidat 85° C. to perform acid precipitation, whereby there was produced2-hydroxynaphthalene-3-carboxylic acid at a rate of 44.8 kg/hr. Theyield based on sodium 2-naphtholate was 47.7%, and 2-naphthol wasrecovered at a rate of 37.3 kg/hr, with the selectivity being 99.4%.

EXAMPLE 5

In a pressure reaction vessel were charged 100 g of potassium phenolate,35 g of phenol and 500 g of a mixture of hydrogenated triphenyls, and areaction was allowed to proceed at 250° C. and at a carbon dioxidepressure of 7 kg/cm² (G) for 20 minutes, with stirring. The reactionmixture was cooled and charged into 200 ml of water, followed byseparation into the reaction medium layer and the water layer at 60° C.The water layer was made acid with dilute sulfuric acid to give 81.6 gof p-hydroxybenzoic acid (having a purity of 99%). The yield based onpotassium phenolate was 77.3%, and the recovered potassium phenolate was21.0 g, with the selectivity being 99.7%.

What is claimed is:
 1. A process for producnig p-hydroxybenzoic acid or2-hydroxynaphthalene-3-carboxylic acid which comprises reacting a liquidmixture consisting of (A) potassium phenolate or sodium β-naphtholate,(B) free phenol or free β-naphthol and (C) a triphenyl or a hydrogenatedtriphenyl wherein the molar ratio of (B) to (A) is 0.1 to 2.0 and theweight ratio of (C) to (A) is 1 to 5 with carbon dioxide, said liquidmixture being maintained in the liquid state throughout the reactionwith carbon dioxide.
 2. The process of claim 1 for producingp-hydroxybenzoic acid wherein the liquid mixture consists of (A)potassium phenolate, (B) phenol and (C) triphenyl or hydrogenatedtriphenyl.
 3. The process of claim 1 for producing2-hydroxynaphthalene-3-carboxylic acid wherein said liquid mixtureconsists of (A) sodium β-naphtholate, (B) free β-naphthol and (C)triphenyl or hydrogenated triphenyl.
 4. The process of claim 1 whichfurther comprises after conclusion of said reaction, separating thetriphenyl or hydrogenated triphenyl reaction medium containing unreactedpotassium phenolate or sodium β-naphtholate dissolved therein andrecovering the dissolved potassium phenolate or sodium β-naphtholate. 5.The process of claim 1 which further comprises, after conclusion of saidreaction, adding water to the reaction mixture, adjusting the pH of theresulting mixture to separate a water layer having the free phenol orfree β-naphthol dissolved therein, and extracting the phenol orβ-naphthol with an organic solvent.